Re: [PATCH v2 11/12] hw/virtio/virtio-mem: register legacy-guest variant with is_available

["Daniel P. Berrangé" <berrange@redhat.com>]

On Sun, Nov 01, 2026 at 12:40:06AM +0800, Yonggang Luo wrote:
> virtio-mem decided in class_init and realize whether x86 guests can
> leave unplugged memory accessible. Register a second virtio-mem type
> that adds virtio_mem_legacy_guests_properties and sets
> VirtIOMEMClass.has_legacy_guests. Select the two with
> target_base_i386() and target_not_base_i386().
> 
> Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
> ---
>  hw/virtio/virtio-mem.c         | 52 +++++++++++++++++++++-------------
>  include/hw/virtio/virtio-mem.h |  2 ++
>  2 files changed, 34 insertions(+), 20 deletions(-)
> 
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index ee6a0c206af..ab2864d18c3 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -15,6 +15,7 @@
>  #include "qemu/cutils.h"
>  #include "qemu/error-report.h"
>  #include "qemu/units.h"
> +#include "qemu/target-info.h"
>  #include "qemu/target-info-qapi.h"
>  #include "system/memory.h"
>  #include "system/numa.h"
> @@ -35,22 +36,6 @@
>  
>  static const VMStateDescription vmstate_virtio_mem_device_early;
>  
> -static bool virtio_mem_has_legacy_guests(void)
> -{
> -    /*
> -     * We only had legacy x86 guests that did not support
> -     * VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE. Other targets don't have
> -     * legacy guests.
> -     */
> -    switch (target_arch()) {
> -    case SYS_EMU_TARGET_I386:
> -    case SYS_EMU_TARGET_X86_64:
> -        return true;
> -    default:
> -        return false;
> -    }
> -}
> -
>  /*
>   * Let's not allow blocks smaller than 1 MiB, for example, to keep the tracking
>   * bitmap small.
> @@ -859,7 +844,7 @@ static void virtio_mem_device_realize(DeviceState *dev, Error **errp)
>      rb = vmem->memdev->mr.ram_block;
>      page_size = qemu_ram_pagesize(rb);
>  
> -    if (virtio_mem_has_legacy_guests()) {
> +    if (VIRTIO_MEM_GET_CLASS(vmem)->has_legacy_guests) {
>          switch (vmem->unplugged_inaccessible) {
>          case ON_OFF_AUTO_AUTO:
>              if (virtio_mem_has_shared_zeropage(rb)) {
> @@ -1635,9 +1620,6 @@ static void virtio_mem_class_init(ObjectClass *klass, const void *data)
>      RamDiscardSourceClass *rdsc = RAM_DISCARD_SOURCE_CLASS(klass);
>  
>      device_class_set_props(dc, virtio_mem_properties);
> -    if (virtio_mem_has_legacy_guests()) {
> -        device_class_set_props(dc, virtio_mem_legacy_guests_properties);
> -    }

Again IMHO the conditional property registration is an
unneccessary step. Just fold virtio_mem_legacy_guests_properties
into virtio_mem_properties.

In the realize() method, check virtio_mem_has_legacy_guests()
and reject values that are invalid for the non-x86 targets.


With regards,
Daniel
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